This invention relates to towed sonar arrays, and more particularly, but without limitation thereto, to the jacket that surrounds the acoustic equipment of such an array.
Towed sonar line arrays are deployed in the ocean for military and commercial purposes. These line arrays most commonly use thermoplastic polyurethane (TPU) in a hose-shaped envelope (known also in this art simply as a "hose"). The hose-shaped envelope contains the hydrophone elements and accompanying transmission lines of the acoustic system.
In recent years, the value of towing multiple lines at the same time has become apparent. This technique has introduced problems in the deployment of the arrays. The problems become apparent when the relativity high surface-friction TPU hoses cross over or lay in parallel contact with one another. In these circumstances, deployment can become impossible or can result in tangling of the hoses.
In military applications, some submarines have used a tube adjacent to their hull to store a single sonar line array. To deploy this array, seawater is pumped into the forwardmost end of the stowage tube, and the array is "flushed" out the aft-end of the tube along with seawater. An early attempt to replace this single line array with several smaller ones was not successful because the multiple lines, unable to move relative to one another due to the TPU hose surface friction, would lock up in the bends of the stowage tube and could not be flushed.
The geophysical (seismic) industry now tows multiple-line arrays in their search for oil. This industry has suffered problems deploying the multiple-line arrays from surface ships due to TPU hose surface friction. Current solutions in use by the oil industry are (1) adding an outer layer of polyvinyl chloride (PVC) to the TPU hose or (2) blending TPU and PVC. These combinations resulted in hose surface friction sufficiently lower than that of TPU, so that deploying multiple line arrays using typical geophysical boat deployment techniques (different from that of the submarine), is now relatively free of problems related to hose surface friction. The materials of the geophysical blends, while acceptable for their intended purposes, provide over-all performance that is less than desired for certain applications.
There is thus a need for an acoustic envelope that provides low-friction surface characteristics, while, at the same time, provides improved damping of hydrodynamically generated, array self-noise.